[SPARK-4889] update history server example cmds

Author: Ryan Williams <ryan.blake.williams@gmail.com>

Closes apache#3736 from ryan-williams/hist and squashes the following commits:

421d8ff [Ryan Williams] add another random typo fix
76d6a4c [Ryan Williams] remove hdfs example
a2d0f82 [Ryan Williams] code review feedback
9ca7629 [Ryan Williams] [SPARK-4889] update history server example cmds

conf/metrics.properties.template

@@ -77,8 +77,8 @@
 #   sample    false      Whether to show entire set of samples for histograms ('false' or 'true')
 #
 # * Default path is /metrics/json for all instances except the master. The master has two paths:
-#     /metrics/aplications/json # App information
-#     /metrics/master/json      # Master information
+#     /metrics/applications/json # App information
+#     /metrics/master/json       # Master information
 
 # org.apache.spark.metrics.sink.GraphiteSink
 #   Name:     Default:      Description:

core/src/main/scala/org/apache/spark/deploy/history/HistoryServer.scala

@@ -158,11 +158,12 @@ class HistoryServer(
 
 /**
  * The recommended way of starting and stopping a HistoryServer is through the scripts
- * start-history-server.sh and stop-history-server.sh. The path to a base log directory
- * is must be specified, while the requested UI port is optional. For example:
+ * start-history-server.sh and stop-history-server.sh. The path to a base log directory,
+ * as well as any other relevant history server configuration, should be specified via
+ * the $SPARK_HISTORY_OPTS environment variable. For example:
  *
- *   ./sbin/spark-history-server.sh /tmp/spark-events
- *   ./sbin/spark-history-server.sh hdfs://1.2.3.4:9000/spark-events
+ *   export SPARK_HISTORY_OPTS="-Dspark.history.fs.logDirectory=/tmp/spark-events"
+ *   ./sbin/start-history-server.sh
  *
  * This launches the HistoryServer as a Spark daemon.
  */